Electronic tremulant system



June 11, 1963 T. .1. GEORGE 3,093,700

ELECTRONIC TREMULANT SYSTEM Filed Sept. 21, 1959 2 Sheets-Sheet 1 PIC-1.2

V\BRATO SIGNAL INPUT SIGN AL.

OUTPUT S\GNAL ACOUSTIC SIGNAL W INVENTOR.

June 11, 1963 Filed Sept. 21, 1959 T. J. GEORGE ELECTRONIC TREMULANT SYSTEM 2 Sheets-Sheet 2 7 Z5 20 Y TREMULANT z A AMP x cuzcurr K 3| 3% TONE. GEN. 25

28 26 27 Y 35 35 4 X 1 l TREMULANT MR w CIRCUIT & 30 A 3!: S L TONE. GEN.

INVE TOR.

United States Patent Oii ice 3,093,700 Patented June 11, 1963 3,093,700 ELECTRONIC TREMULANT SYSTEM Thomas J. George, Los Angeles, Calif. (11671 Victory Blvd., North Hollywood, Calif.) Filed Sept. 21, 1959, Ser. No. 841,244 4 Claims. (Cl. 841.22)

This invention relates in general to electronic organs, and in particular to a simplified tremulant system for such instruments.

Nearly all electronic organs now commercially available are equipped with some form of musical vibrato instead of tremultant. Vibrato is commonly defined as a periodic change in the pitch of the tones of the instrument, while tremulant is defined as a periodic change in the amplitude of the tones, or in brief, vibrato is frequency modulation, and tremulant is amplitude modulation of the musical tones. The frequency of these periodic changes, or beats, iies usually between approximately five and one half to seven and one half cycles per second.

In the pipe organ, the tremulant or vibrato is usually effected by a periodic change in the pressure of the wind which is blowing the pipes. This causes both the pitch and the loudness of the pipe tone to change periodically. It is apparent therefore, that to more nearly approach the musical effect produced by the pipe organ, the tones of the electronic organ should cyclically change in both pitch and loudness, and this result will in fact be achieved if both vibrato and tremulant are present in the tones of the electronic organ.

In the entertainment type, or so called theatre pipe organ, it is customary to provide, for certain effects, a very heavy tremulant, and in fact this has come to characterize this type organ. This type of theatrical tremulant is very popular, especially when used with certain types of tone, such as flute. Some types of organ pipes, such as string or reed, with a given change in wind pressure, will produce more change in pitch than other types. On the other hand, other pipes such as flutes produce more change in amplitude and less pitch change, with a given change in wind pressure.

In electronic organs, usually the same vibrato is applied to all voices, and in most of these organs little or no tremulant is present other than that which occurs as a result of acoustic room pattern.

Apparently because of the frequency response characteristics of the human ear, as well as other psychological factors, more actual change in frequency is required with flute tone, than with string tone for example, to produce an equivalent subjective vibrato effect. This is probably due to the fact that flute tone is relatively pure, with but few harmonics. String tone is very bright, with complex harmonic structure, and it is probable that the ear more readily perceives the pitch movement of the higher order harmonics of the bright string tone. However it is observable, that when using flute tone, a heavy tremulant is subjectively practically equivalent to a heavy vibrato, and this is consistent with the heavy tremulant used with flute voices in the theatre pipe organ.

The limiting factor in the maximum amount of vibrato which is useful is an apparent out of tuneness which occurs when the periodic pitch change becomes too great. To some extent this is a matter of personal taste, and will vary for different individuals. However, it is certainly true that a too heavy vibrato is more objectionable with a bright tone than with a pure tone. This leaves many listeners with the feeling that the heaviest permissible vibrato for bright voices in the electronic organ, is still not heavy enough for pure voices such as flute and even diapason. In other words, for theatrical effects, the

heaviest permissible vibrato may still leave the listener with the feeling that an even heavier beat could be desirable. Thus in accordance with this invention, if when the maximum permissible vibrato is in use, a synchronized tremulant beat of a type to be disclosed herein, is added to the vibrato beat, a heavy theatrical effect will result. Furthermore this heavy tremulant heat will not contribute to the out of tuneness mentioned above, because the tremulant is not a change in pitch, but a change in amplitude. 1

However, to add to the vibrato a tremulant of the type wherein the amplitude of the signal merely rises and falls cyclically, does not result in much improvement. Accordingly, a tremulant system is herein disclosed, wherein the organ signal is amplitude modulated completely, and at the same time the phase of the signal is reversed twice in every tremulant cycle. This system should not be confused with various phase shift methods of the prior art. The present invention does not shift the phase and there is no change in velocity of vector rotation to any significant degree. Rather there is a complete amplitude modulation accompanied by a reversal of phase, and this will be more fully explained.

Hereinafter the normal tremulant rate will be referred to as six cycles or beats per second, but it will be understood that any generally accepted tremulant rate may be used, and may lie anywhere between approximately five and one half to seven and one half cycles per second.

So far as I am aware no intrument has heretofore been devised in which vibrato or frequency modulation, and tremulant or amplitude modulation, are both provided, and which may be used separately or together in selected amounts.

Thus in accordance with the invention, a principal object is to provide means whereby a tremulant may be used separately or in conjunction with the normal vibrato of an electronic organ, and to a degree selected by the player.

Another object is to provide means for a so called stereophonic tremulant which obviates the monotony of a simple amplitude tremulant, by causing a continuous three dimensional change in acoustic room pattern. This stereophonic tremulant has as one of its principal features the production of a secondary tremulant beat in addition to the normal or primary tremulant beat. The function and operation of this secondary beat is described in detail in my United States Patent 2,780,302, and in that patent the effect is produced by purely mechanical-acoustical means. In the present disclosure the effect is produced by electro-acoustical means. In brief, it has been observed that part of the heavy tremulant beat of the theatre organ is occurring at double frequency or about twelve beats per second. This beat rate may be thought of as being superimposed upon the normal six cycle beat, or

. it may be considered to be a light secondary beat spaced alternately in time with the normal primary beat.

In the present invent-ion, the tremulant effect is the result of acomposite acoustic signal. In part of this signal which is radiated from one loudspeaker, the signal voltage is caused to reverse in phase approximately twelve times per second, or twice in every normal tremulant cycle. The other part of the signal which is radiated from a second speaker, is of constant unchanging phase and amplitude. The two parts are thus combined acoustically. During one half the tremulant cycle, the two parts are in phase and are additive. During the other half cycle the signals are of opposite phase, and tend to cancel one another. When the two parts are thus combined acoustically, the addition and cancellation of the signals occurs in the air, with a pleasing three dimensional or stereo effect. 7

Another object therefore is to provide simplified means for reversing the phase of part of' the signal twice in every tremulant cycle.

Another object is to electrically combine the phase reversing signal with the steady unmodified signal to' produce a pleasing tremulant.

Other objects will appear from the following description, reference being had to the accompanying drawings in which:

FIGURE 1 is a schematic of the circuit used for reversingthe phase of the organ signal in one form of the invention.

FIGURE 2 is illustrative of the various signal envelopes employed in the practice of the invention.

FIGURE 3 is a block diagram of a preferred form of the invention.

FIGURE 4 is a block diagram of a modified form of FIGURE 3.

Referring to FIGURE 1, a phase reversing circuit is shown which operates as follows. A multi grid tube such as a type '6BY6 is shown at 1. This tube is connected as a variable gain audio amplifier. Its cathode 2 is grounded through resistor 3, which is bypassed by means of capacitor 4. Theanode 5 is connected by means of plate resistor 6 to B plus supply 7. The screen grid 8 is connected to the B plus supply 7 through resistor 9, and is bypassed to ground' by means of capacitor 10. The signal grid 11 is connected through resistor 12 to input terminal Z, and is returned to ground through resistor 13. The injector grid '14 is connected through capacitor 15 and resistor 16 to vibrato signal input terminal Y, and is returned to ground through resistor 17 and capacitor 18 in parallel. The anode 5 connects to output terminal X through capacitor 19 and adjustable voltage output control 22. Anode 5 is also connected to input terminal Z through capacitor 20 and variable resistor 21 connected in series.

As the circuit is normally used, the output signal from the organ tone generator is connected to input terminal Z. In most electronic organs, a low frequency oscillator is provided which generates a vibrato signal of approximately six cycles per second. The output signal from this oscillator is used within the organ for effecting a vibrato or frequency modulation of the signals from the tone generators in the organ. A connection is made, as shown, between the six cycle oscillator'39 and'the vibrato signal input terminal Y. This connection provides a six cycle control voltage which is used to vary the amplification of tube 1. In order to obtain a tremulant which is synchronized with'the organ vibrato, it is necessary to obtain the six cycle control signal from the organ vibrato circuit. However, it should be understood that if it is not desired to synchronize the tremulant with the vibrato, or if the tremulant'circuit is to be used with an instrument which does not have a vibrato, such as a guitar, piano, or reed organ, then the six cycle control signal may be taken from any convenient so'urce.

Resistors 16 and 17 are selected so that the vibrato control signal at the injector grid 14 is approximately two volts. The voltage at grid 14 will thus rise and fall six times per second. When it is maximum in a positive direction, the gain of tube '1' will be 'a' maximum. When the voltage at grid 14 is maximum in a negative direction the gain of tube 1 will be zero and the tube will be cut off.

In FIGURE 2, at curve A is shown one cycle of the vibrato control voltage, and the time interval is approximately one sixth second. Immediately below, curve B shows how the relative gain of the tube varies with vibrato signal voltage, reaching a maximum during the positive half cycle, and being reduced to zero during the negative half cycle. Since the tube is cut off during the negative half cycle, the output signal appearing at anode 5 is discontinuous. The signals from the organ tone the anode circuit from the grid 11.

generator are connected through the voltage divider, comprising resistors 12 and 13, to input grid 11 of tube 1. During the positive half cycle of vibrato voltage, the tube will amplify the organ signal, and an amplified output signal will appear at anode 5., and hence at output terminal X. This signal will have the appearance of a completely modulated envelope similar to that shown in curve C. This curve indicates that there is no output signal during the negative half cycle of vibrato signal voltage. The shaded portion of the envelope above the zero axis represents the area of negative swing of the modulated organ signal voltage, and the unshaded portion below the axis is the area of positive swing of this voltage. The frequency of the organ signal is not important. Curve D shows the envelope of the unmodulated organ signal appearing at the input terminal Z. Note that the unshaded positive area is above the axis and the shaded negative area is below the axis, which is the reverse of curve C. A part of the direct organ input signal is carried from input terminal Z to the anode 5 through variable resistor 21 and blocking capacitor 20, and the amount of direct unmodulated organ signal which appears at the anode is controlled by the selected value of resistor 21. It will thus be understood that the signal appearing at the anode 5, and at the o-utputterminal X at any moment is a composite signal, which is the instantaneous algebraic sum of the direct organ signal, and the amplitude modulated organ signal. Because of the phase inverting action of tube 1, the modulated organ signal is opposite in phase to the direct organ signal, which undergoes no change in phase. This is illustrated in the envelope curves C and D in FIGURE 2. The composite algebraic sum of curves C and D is shown in curve E. Assume that the maximum amplitude of the modulated output signal, curve C, is approximately twice the amplitude of theunmodulated inputsignal, curve D. Then, since the signals are opposite in phase, cancellation will take place during the first half of the tremulant cycle, the interval from r to s. The resultant signal will be of half the amplitude of the modulated signal C and of the same phase.

During the second half of the tremulant cycle, the interval from s to t, the tube is cut off, and no modulated output signal appears at the anode 5, but only the direct organ signal. The direct signal appearing at the anode and output terminal X during the second half of the tremulant cycle will therefore be of approximately equal amplitude, but of opposite phase to that which appears during the first half cycle. The result is the double lobed envelope of curve E. This curve illustrates that the composite output signal from the tremulant circuit rises to a peak every second, or twice in every tremulant cycle, and that the first and second peaks are of opposite phase. The relative amplitudes of the first and second peaks are controlled by means of variable resistor 21, and the peaks are adjusted to be of approximately equal amplitude when it is desired to obtain the Y secondary tremulant beat described in the previously men tioned patent.

The voltage divider comprising resistors 12 and 13 is an important aspect of the invention and its function is explained as follows. Its primary purpose is to isolate If this were not done, then the feed-forward path through resistor 21 and capacitor 20 would form a very effective negative feedback means, and the tube could not function in the manner described. This divider therefore is a very important part of the tremulant circuit. The second purpose of the divider is to reduce the input voltage to grid 11 in order to avoid distortion. Capacitor 19 is selected to be of a value small enough to attenuate any six cycle component in the output voltage, yet not small enough to seriously impair the bass notes of the organ tones.

. t The following table gives values for the components which are used in the circuit of FIGURE 1:

FIGURE 3 is a block diagram showing the manner in which the tremulant circuit of FIGURE 1 will normally be used with an electronic organ. An electronic organ is indicated at 23, having a keyboard 24, a tone generator 25, an amplifier 26, and an acoustical transducer such as speaker 27. The tone generator has a signal output terminal 31 which is connected to the input terminal Z of the tremulant circuit 33. The tone generator also has a vibrato signal voltage output terminal 30 which is connected to the vibrato signal input terminal Y of the tremulant circuit. The organ amplifier 26 has an input terminal 28 which is connected to the tremulant circuit input terminal Z by means of lead 38. The output of the amplifier 26 is connected to organ speaker 27. The output terminal X of the tremulant circuit is connected to the input terminal 36 of a second amplifier 34. The output of amplifier 34 is connected to a speaker 35.

In operation of the circuit of FIGURE 3, the signals from the organ tone generator are amplified and reproduced by the organ amplifier and speaker 26 and 27. The tone generator output signals are simultaneously modulated by means of the tremulant circuit 33 in the manner previously described, and the modulated output signals are amplified and reproduced by means of the amplifier and speaker 34 and 35. Speaker 35 may be mounted in the organ with speaker 27, or it may be mounted in a separate tone cabinet.

An unmodu-lated organ signal represented by curve D of FIGURE 2 will be reproduced by organ speaker 27, and the double lobed signal of curve E will be reproduced by speaker 35. The relative loudness of the two signals may be adjusted by means of output control 22 of FIGURE 1. When they are of about equal loudness, a heavy tremulant beat will be heard which can be represented approximately by curve F of FIGURE 2. This curve is representative of the composite modulated acoustic signal envelope occuring at some point in the listening area, and it may be observed by the use of a microphone and an oscilloscope. However, it is only representative, since acoustic room pattern variations will change the curve shape in different parts of the listening area. Note also that the phase position during the first half of the tremulant cycle is reversed during the second half of the cycle. These two efliects combine to produce a stereo-tremulant efiect because the room pattern is never the same at any given instant for the listeners two ears, and the result is a very pleasing three dimensional movement of the organ tones.

The degree of tremulant employed may be selected by the adjustment of tremulant output control 22, and the degree of the secondary beat efiect may be selected by means of control 2.1.

If it is desired for the sake of economy, not to incorporate the stereo feature, this may be done by eliminating amplifier and speaker 34 and 35. If this is done then lead 38 should be disconnected from tremulant input terminal Z, and connected instead to output terminal X, as shown in FIGURE 4. With this arrangement it may be desirable to readjust slightly control 21. This will make the secondary tremulant beat less prominent, by making one or the other lobe larger in curve B. It 'will be seen that by adjusting this resistor to a small value, the tremulant beat may be eliminated, because the modulating circuit is bypassed. Thus with this arrangement, variable resistor 21 controls the degree of tremulant, and amplifier and speaker 26 and 27 reproduce the organ tones, either with or without tremulant.

In using this tremulant system with an electronic organ, it will be apparent that many possible combinations of tremulant and vibrato may be used. The organs own vibrato may be used without tremulant. The tremulant may be used in varying degrees with the organ vibrato turned off. The tremulant may be used in combination with the organ vibrato, and when they are both set to maximum a very heavy theatrical beat will be obtainable.

What are considered to be the novel features of this disclosure are:

(1) Means for providing in an electronic organ, both tremulant and vibrato, which may be used separately or in combination.

(2) A simple one tube circuit capable of reversing the phase of the organ signal approximately twelve times per second.

(3) Means for providing a tremulant having a secondary beat.

(4) Means for combining a modulated signal of one phase with a steady signal of opposite phase to obtain a tremulant.

(5) Means for acoustically combining an amplitude modulated signal of one phase with a steady signal of opposite phase for obtaining a stereo tremulant efiect.

It will be understood that while I have shown and described preferred embodiments of my invention, it will be apparent to those skilled in the art that numerous variations and modifications may be made, such as the use of transistors, varistors, or other modulating means, without departing 'from the basic principles of the invention. I therefore desire, by the following claims, to include Within the scope of my invention all such equivalent or similar constructions whereby substantially the same results may be obtained by substantially the same or equivalent means.

Having thus described my invention, I claim as follows:

1. A tremulant circuit for musical instruments comprising an audio signal source, a vibrato oscillator signal source, a single stage variable gain amplifier having an output and first and second inputs for combining said audio signal and said vibrato oscillator signal to produce a discontinuous signal of opposite phase from said audio signal, means connecting said audio signal source to said first input, means connecting said vibrato oscillator source to said second input and a feed-forward path connecting said source of audio signals to the output of said variable gain amplifier without changing the phase of said audio signal, whereby said discontinuous signal and said audio signal are combined to produce a tremulant signal of desired characteristic.

2. A tremulant circuit for musical instruments comprising an audio signal source, a vibrato oscillator signal source, a single stage variable gain amplifier having an output and first and second inputs for combining said audio signal and said vibrato oscillator signal to produce a discontinuous signal of opposite phase from said audio signal, means connecting said audio signal source to said first input, means connecting said vibrato oscillator source to said second input, a feed-forward path connecting said audio signal source to the output of said variable gain amplifier without changing the phase of said audio signal, and means effectively isolating said feedforward path from said amplifier toprevent feedback, whereby said discontinuous signal and said audio signal are combined to produce a tremulant signal of desired characteristic. I

3. In an electronic organ an audio signal source, a vibrato oscillator signal source, first amplifier means having an output and a plurality of inputs for combining said audio signal and said vibrato oscillator signal to produce a discontinuous signal of opposite phase from said audio signal, a feed-forward path connecting said audio signal source to the output of said first amplifier means Without changing the phase of said audio signal, second amplifier means, means connecting said first amplifier output to said second amplifier means, and acoustical transducer means connected to said second amplifier means to produce a musical sound having a desired tremulant effect.

4. In an electronic organ an audio signal source, a vibrato oscillator signal source, first amplifier means having an output and a plurality of inputs for combining said audio signal and said vibrato oscillator signal to produce a discontinuous signal of opposite phase from said audio signal, a feed-forward path connecting said audio signal sourceto the output of saidfirst amplifier means Without changing the phase of said audio signal, second and third amplifier means, means connecting said audio signaltsource to said second amplifier means, means connecting saidqfirst amplifier output to said third amplifier means,,first. acoustical transducer, means connected to said second amplifier means, and, second acousticaltransducer means connected to said third amp1ifier means, whereby the acoustical, signals generated by saidtransducers will combine to produce a desired stereo tremulant efiect.

References Cited in the file of this patent UNITED PATENTS 2,093,223 Yasmashita Sept. r1 4, 1937 2,148,478, Kock Feb. 28, 1939 ,3 4 une 10,1

,.---*r'r. 2, 8 v 4 bl 1.944 2,758,204 Norby Aug, 7, 1956 2,817,708 Fender Dec. 24, 1957 2,835,814 Dorf May 20, 1958 2,845,491 Bertram July 29, 1958 2,883,625 Sparks Apr. 21, 1959 

1. A TREMULANT CIRCUIT FOR MUSICAL INSTRUMENTS COMPRISING AN AUDIO SIGNAL SOURCE, A VIBRATO OSCILLATOR SIGNAL SOURCE, A SINGLE STAGE VARIABLE GAIN AMPLIFIER HAVING AN OUTPUT AND FIRST AND SECOND INPUTS FOR COMBINING SAID AUDIO SIGNAL AND SAID VIBRATO OSCILLATOR SIGNAL TO PRODUCE A DISCONTINUOUS SIGNAL OF OPPOSITE PHASE FROM SAID AUDIO SIGNAL, MEANS CONNECTING SAID AUDIO SIGNAL SOURCE TO SAID FIRST INPUT, MEANS CONNECTING SAID VIBRATO OSCILLATOR SOURCE TO SAID SECOND INPUT AND A FEED-FORWARD PATH CONNECTING SAID SOURCE OF AUDIO SIGNALS TO THE OUTPUT OF SAID VARIABLE GAIN AMPLIFIER WITHOUT CHANGING THE PHASE OF SAID AUDIO SIGNAL, WHEREBY SAID DISCONTINUOUS SIGNAL AND SAID AUDIO SIGNAL ARE COMBINED TO PRODUCE A TREMULANT SIGNAL OF DESIRED CHARACTERISTIC. 